1. Field of the Invention
This invention relates to a high temperature oxidation and corrosion resistant coated nickel-base superalloy article comprising (a) a nickel-base superalloy article, and .[.(b) a first.]. .Iadd.adjacent thereto (b) a .Iaddend.CoCrAl(Y) coating .Iadd.having a substantially uniform .Iaddend.composition .[.consisting essentially.]. .Iadd.composed .Iaddend.of, on a weight basis, approximately 26-32% chromium, 3-9% aluminum, 0-1% yttrium, the rare earth elements, platinum or rhodium, and the balance .[.nickel.]. .Iadd.cobalt and impurities ordinarily associated with the aforementioned constituents.Iaddend.. An aluminide overcoating can be applied to the CoCrAl(Y) coated superalloys and constitute another embodiment of my invention.
2. Description of the Prior Art
Evans et al. in U.S. Pat. No. 3,676,085 describe coated nickel-base superalloys wherein the coating composition consists essentially of, on a weight basis, 15-40% chromium, 10-25% aluminum, 0.01-5% yttrium or the rare earth elements and the balance cobalt. Evans et al. .[.teache.]. .Iadd.teach .Iaddend.that when the aluminum content of the CoCrAl(Y) coating is below about 10% there is insufficient aluminum present in the coating system to provide the desired long term durability in the coating.
Unexpectedly, I have found that nickel-base superalloys when coated with CoCrAl(Y) coatings having an aluminum content of less than 10% have outstanding physical and chemical properties, i.e. significant oxidation and corrosion resistance and high coating-substrate interface integrity. These outstanding properties are not associated with nickel-base superalloys when coated with the coating systems described by Evans et al. referenced above.